Buried in President Donald Trump's budget proposal released Thursday was an opening salvo against so-called sanctuary cities, local jurisdictions he promised to punish for refusing to cooperate with deportation officers.

Trump wants to slash $210 million in federal reimbursements to state and local jails that hold immigrants convicted of crimes while in the country illegally. The Trump administration called the program "poorly targeted," adding that two-thirds of the money goes to only a handful of states, including California and Illinois, "for the cost of incarcerating certain illegal criminal aliens."

The money, awarded by the Department of Justice, can make up a sizable portion of budgets for state and local police and sheriff's departments.

Trump, who promised weeks before he was elected to "cancel all federal funding to sanctuary cities," appears to be using it as a cudgel to force those local governments to comply with his administration's efforts to deport people who are in the U.S. illegally.

"They are not working with the feds to try to address the immigration problem, so why should they be reimbursed for the costs of unsuccessful federal immigration enforcement?" said Mark Krikorian, executive director of the Center for Immigration Studies, which favors restrictive immigration policies.

The proposal is part of Trump's effort to fulfill his campaign pledge to toughen border security. The president immediately began a widespread crackdown on illegal immigration when he took office, issuing executive orders that targeted for deportation all 11 million people estimated to live in the U.S. without authorization.

The "sanctuary cities" designation has existed for decades and is applied differently by each place that claims it, but generally it means that local political and law enforcement leaders have rejected taking part in immigration enforcement, saying it makes immigrants less likely to report crimes or help police conduct investigations.

A California law signed by Gov. Jerry Brown in 2013 bars state police from holding someone for immigration agents unless the suspect has been charged or convicted of a serious crime such as drug trafficking, child abuse or gang activity.

Trump often said during the campaign he would cut federal funds to cities, including Los Angeles and Chicago, that routinely refuse to hold people in local jails until immigration officials can take them into custody.

His budget proposed eliminating the money from the State Criminal Alien Assistance Program, the Justice Department program that distributes the reimbursements. The cut would nearly zero out its funding for those types of payments.

The California state government received $50.6 million in reimbursements under the program last year, according to the Department of Justice. The Los Angeles County Sheriff's Department received $6 million. The Illinois Department of Corrections brought in $4.7 million, and Cook County, home to Chicago, received $1.3 million.

Trump would use the savings in part to ramp up immigration enforcement personnel in the Department of Justice. His budget called for hiring 75 new immigration judges, bringing the total to 449, as well as adding 60 federal prosecutors to focus on border enforcement and 40 more deputy U.S. marshals to aid in the "the apprehension, transportation, and prosecution" of those in the country illegally.

Democrats and others condemned Trump's proposal.

"This cut is utterly illogical and would force state and local law enforcement to divert funds from hiring and training officers," Sen. Dianne Feinstein of California, the top Democrat on the Senate Judiciary Committee, said in a statement.

"Local law enforcement should not be punished for Congress' failure to pass a comprehensive immigration reform bill," Feinstein said.

The reimbursements to jails have been part of a cat-and-mouse game between the White House and Congress before.

Previous presidents, including Barack Obama, have proposed eliminating funding for the program, only to have lawmakers preserve it in appropriations bills. Obama's budget last year sought to divert the funding to juvenile justice programs, crime statistics research and body cameras for local police, among other initiatives.

"Sanctuary cities are nullifying federal law, taking federal law into their own hands," said Krikorian, who sent policy proposals to the Trump transition team.

Nonetheless, Krikorian expects Congress will preserve the money for local jails.

"It might be useful to keep because then you can use it as a sweetener for some jurisdictions not to be sanctuary cities," he said.

Denying funding to some states and cities and not others could open the Trump administration to lawsuits, warned Chris Rickerd, an expert on border security at the American Civil Liberties Union. Slashing the entire fund may be an easier way to get the same result, he said.

"This is a test for what he can touch in terms of grant funding," Rickerd said.

Trump has called for local officials to be required to identify people who are in jail and could be deported when they are released.

During the campaign, Trump also met repeatedly with people whose loved ones were killed by immigrants in the country illegally, and he has told aides that he sees taking on sanctuary cities as necessary to improve public safety.

The July 2015 shooting of Kathryn Steinle, 32, on a pier at San Francisco's Embarcadero brought the issue of local cooperation with immigration officials into the national spotlight, and Trump cited her on the campaign trail in calling for stricter immigration enforcement.

The man arrested in her death had been jailed on an immigration law violation after returning to the U.S. despite being deported five times. He was released from custody months before the shooting after San Francisco prosecutors decided not to pursue a decades-old bench warrant in a marijuana case.

When Trump addressed Congress last month, four people whose relatives were killed by people in the country illegally sat in the House gallery. The president called them "very brave Americans whose government failed them."